The front wheel of a motorcycle is usually linked to the frame by a pair of fork tubes. These tubes house the front suspension and usually include springs and compartments filled with fork oil to act as a shock absorber, which protects the rider from bumps and vibrations as the vehicle travels uneven surfaces.
The most common form of fork commercially available is a telescopic fork which uses fork tubes which contain the suspension components (coil springs and damper) internally. This design is simple and inexpensive to manufacture, and relatively light compared to designs based on external components and linkage systems.
The systems that rely on using fork oil as a damper, use oil seals to contain the oil in a space within the fork tubes. This oil needs to be replenished or replaced periodically and to do this, the structure needs to be at least partially disassembled, which usually involves removing or replacing the oil seals. These seals generally take the form of annular rings which fit around the central tube and which seat in position to contain the oil without leakage. In order to ensure that these seals are properly seated, generally a fork seal driver is used. This fork seal driver is generally a cylindrical structure which encircles the central tube and slides along its length until it contacts the fork seal and drives it to seat properly. Thus, it acts as a form of small slide hammer.
FIG. 1 shows the principle elements of a fork tube assembly 1 with a fork seal driver 2 in place. The fork inner leg 3 has a first end 5 including the slider bushing 17 which slides within the fork outer leg 4. At the second end 6 of the fork inner leg 3, there is a fork lug 7. The fork outer leg 4 has a fork cap 8 at its first end 9, and its second end 10 includes a fork seal seat 12, which includes a backup ring, an oil seal stopper groove 11, and a guide bushing 13. The fork seal 14 slides into the second end 10 of the fork outer leg 4 against the fork seal seat 12. The oil seal stopper 15 then is pressed against the fork seal 14 into the oil seal stopper groove 11 to help maintain the fork seal's 14 position.
The fork seal 14 seats generally in a plane 18 perpendicular to the longitudinal axis 19 of the fork tube assembly 1. The driver 2 ideally contacts all points of the fork seal 14 in this plane 18 and moves them in the direction of the longitudinal axis 19 together, so that the fork seal 14 is pressed properly into the fork seal seat 12 and the oil seal stopper 15 seats properly against the oil seal stopper groove 11, and both are not damaged. In order for the driver 2 to best travel in this length axis 19 direction without skewing or binding, the diameter of the inner bore 16 of the driver 2 closely matches the diameter of the fork inner leg 3 along which it travels. The fork inner leg 3 may preferably have attached fork lug 7 still in place, which has a larger diameter. It is generally undesirable to remove the fork lug 7 for this operation, and the inner bore 16 diameter of the driver 2 does not allow the driver 2 to be slipped onto the end of the fork tube assembly 1 past the fork lug 7 without further disassembly.
Instead, as shown in FIG. 2, fork seal drivers 2 are generally configured as two half-cylindrical pieces 30 which mate together around the fork inner leg 3, to form a cylindrical body 32. The half-cylindrical pieces 30 are fitted together by means of pins 34 on a first half-cylindrical piece 36, which is a male part 38, which fit into matching holes 40 in the second half-cylindrical piece 42, thus a female part 44. These half-cylindrical parts 30 are generally machined as a complete cylindrical piece, and then cut in half. The first piece 36 has pins 34 installed, and the second piece 42 has holes 40 bored to match the placement and length of the pins 34.
Ideally, the two half-cylindrical pieces 36, 42 reunite to re-form the original cylindrical body configuration 32, in which a bottom driver edge 46, forms a uniform contact plane 48 for driving and seating the fork seal 14. The driver 2 also preferably includes an outer bore step 50 and an internal bore step 52, which help to carry the fork seal 14 and drive it into the fork seal seat 12 squarely.
However, it can be appreciated that splitting the original cylindrical piece 32 into two half-cylindrical pieces 36, 42 must be a fairly precise operation, and that installing the mating pins 34 and mating holes 40 also requires fairly tight tolerances. The necessity for such tight tolerances can produce parts that are rather costly and require precise manufacturing processes. Further, each separate part must be produced with these same tight tolerances, thus the manufacturing and machining must be repeatably precise, or else there can be an expensively high failure rate for the parts.
In addition, the pins and holes in the male and female parts are included merely to locate the pieces properly, and are not used to hold them in place during the driving operation. Instead the parts are generally held by the user's hand, as the driver slides up and down, and can easily come apart completely if not held correctly. Worse yet, the parts may come apart slightly, but not completely, so that a uniform contact surface is not formed by the lower edge of the driver. An uneven contact surface may cause damage to the seals and or the outer fork leg, whereby they may need to be replaced entirely, at greater expense and expenditure of time.
Yet further, as the driver is fashioned into two separate male and female parts, production costs are increased compared to a situation where there is only one uniform kind of part, and two of these uniform parts are held together in a different, more secure manner.
Thus, there is a need for a fork seal driver which is easier and less costly to manufacture, which may not use separate male and female mating parts, and which is held together securely to minimize damage to seals as they are driven.